1. Field of the Invention
The present invention relates to an original disk fabrication method, a magnetic recording medium manufacturing method and a magnetic recording medium.
2. Related Art
In the technical trend toward the higher density of the magnetic disk (hereafter referred to as hard disk as well), a medium structure on which a magnetic part region issuing a magnetic signal is divided by nonmagnetic parts, i.e., the so-called medium structure of discrete type as described in JP-A 2004-110896 (KOKAI) is proposed. In additions a patterned medium on which a data track part is not only divided by grooves in the circumferential direction but also divided every data bit as described in IP-A 2006-79827 (KOKAI) is proposed. A method of forming dots by using self-organization of block copolymer and processing the dots is also proposed in IP-A 2006-79827 (KOKAI). Especially in the case of a wide area, however, it is considered to be difficult to control the atmosphere so as to arrange dots in good order As to this problem, it is proposed to use a guide as described in Japanese Patent No. 3793040. It is considered to be simple to form up to dot patterns by the electron beam lithography.
On the other hand, a technique of transferring a mold pattern having a size of 200 nm or less onto a film, called nano imprint lithography is described in U.S. Pat. No. 5,772,905. A technique of transferring a discrete-type magnetic disk pattern by using the imprint method is described in JP-A 2003-157520 (KOKAI). In JP-A 2003-157520 (KOKAI), it is described that a medium pattern is formed by using a stamper set up on the basis of an original disk which is fabricated by using the electron beam lithography technique. However, the electron beam lithography technique and the stamper pattern are not described.
In general, the magnetic disk apparatus includes within a casing, a magnetic disk taking the shape of a torus-shaped disk, a head slider including a magnetic head, a head suspension assembly which supports the head slider, a voice coil motor (VCM), and a circuit substrate.
The inside of the magnetic disk is divided into concentric tracks cut in round slices. Each of the tracks has sectors obtained by dividing the track every definite angle. The magnetic disk is attached to a spindle motor and rotated. Various digital data are recorded and reproduced by the magnetic head. Therefore, user data tracks are arranged in the circumference direction. On the other hand, servo marks for position control are arranged in a direction so as to stride across the tracks. Each servo mask includes regions such as a preamble part, an address part, and a burst part. Each servo mark includes a gap part besides these regions, in some cases. Each address part is provided with sector number information which changes in the circumference direction and track number information which changes in the radial direction.
As for a stamper original disk for fabricating a magnetic disk of discrete type or bit-patterned type by using the imprint system, it is desired to form both a user data track region (data part) and a servo region simultaneously. Otherwise, one of the regions is added later resulting in difficult positioning and complicated processes.
In fabricating the original disk, its pattern can be formed by exposing photosensitive resin to a chemical beam such as a mercury lamp, an ultraviolet beam, an electron beam and an x-ray beam. However, it is necessary to draw concentric circles. Therefore, the electron beam lithography with deflection added is desirable. Furthermore, it is necessary to couple fine patterns such as hard disk patterns having a track pitch of submicron order with good precision, Therefore, a scheme of moving the stage continuously is more desirable than the step-and-repeat scheme in which the stage is made to stand still when electron beam lithography is conducted and the stage is moved to the next field after all patterns in one field have been drawn.
It is desirable to use an electron beam irradiating apparatus of a continuous stage movement scheme including a moving mechanism to move the stage in one horizontal direction and a rotating mechanism to rotate the stage, from among electron beam irradiating apparatuses capable of drawing concentric circles. In this electron beam irradiating apparatus, a spot beam from one point on a movement axis is applied to the photosensitive resin on the substrate placed on the stage to conduct electron beam exposure. If any external force is not applied to the electron beam for deflection, the distance between the rotation center of the substrate and the electron beam irradiation position changes with time, and consequently a spiral shape is drawn. Therefore, concentric circles can be drawn by deflecting the electron beam while gradually changing the deflection strength (deflection quantity) every rotation in the electron beam exposure process. Here, it is not necessary to draw one track on one circumference, but one track may be formed by drawing on a plurality of circumferences. Because the pattern precision in the radial direction can be improved by doing so. It has a merit in pattern precision in that drawing is conducted with a fine beam diameter, to draw while deflecting the beam by a width of a bit pattern in the radial direction during a movement corresponding to one bit pattern in the circumferential direction when drawing one bit pattern. In general, however, the beam current value in the exposure spot cannot help being made as small as several to several hundreds pA, resulting in great demerit in mass production. It is desirable from the viewpoint of both mass production and pattern precision that the beam current value of an electron beam irradiating apparatus (hereafter referred to as EBR (Electron Beam Recorder) as well) which draws a hard disk pattern of submicron order is in the range of several nA to several tens nA.
When drawing a pattern in the circumference direction by using an EBR, it suffices to bring the beam into the ON state or the OFF state for a time corresponding to a desired length. When drawing a pattern in the radial direction, however, it is necessary to bring the beam into the ON state or the OFF state at a predetermined angle position every circumference.
When forming an original disk pattern of a magnetic disk by using such an electron beam irradiating apparatus, it is necessary to form the address part and other regions simultaneously as described above. As for the address part, however, it is necessary to form a pattern which changes according to its track position and sector position. Because the pattern on the original disk finally becomes the magnetic pattern on a magnetic recording medium and a magnetic signal of position information needs to be sensed in the address part on the magnetic disk. Therefore, it is desired that a signal corresponding to a pattern to be drawn in the address part is automatically calculated and output while it is being changed according to the pattern forming position, from an apparatus (which is hereafter referred to as signal source and also called formatter) for generating a signal which controls rotation, feeding and blanking of an electron beam irradiating apparatus to the electron beam irradiating apparatus.
In the magnetic disk, the bit length at a certain radius is obtained by the relation: the length of the circumference at the radius÷ the number of sectors per circumference÷ the number of bits per sector. The bit length is used to be constant in the address part, the data track part, and other areas. The conventional signal source let a beam go through to the substrate to be exposed, when the bit pattern to be drawn corresponds to bits to be exposed. When the bit pattern to be drawn corresponds to bits which should not be exposed, the conventional signal source applies blanking to prevent the beam from being output. Here, in the address part, both the magnetic part and the non-magnetic part can produce significant magnetic signals. However, the non-magnetic part in the data track part serves as a barrier for preventing magnetic parts from interfering each other, and the non-magnetic part itself has no meaning as a magnetic signal. If each of non-magnetic parts in the data track part in the radial direction is also provided with an area corresponding to one bit as in the conventional art, the recording density decreases to half and the meaning of the change from the conventional in-plane recording scheme to the patterned media scheme made aiming at an increase of the recording density is lost. If on the contrary the bit length is shortened to increase the recording density in the address part as well, deciphering is affected, resulting in operation troubles of the hard disk.